1. Field of the Invention
The present invention relates to an orthodontic appliance to be used in a mouth.
2. Description of the Related Art
The orthodontic appliance is attached to tooth surfaces for orthodontic treatment, and serve to transmit restoring force of an archwire to a root of the teeth.
An orthodontic appliance 70 as shown in FIG. 10 comprises a base 71, a main body 72, an archwire slot 74, and a convertible cap 75. The base 71 is firmly attachable directly or indirectly to teeth. The main body 72 is equipped on one side of the base 71. The archwire slot 74 is shaped in groove along mesiodistal direction in the main body 72, and enables to support an archwire (not shown) therein. The convertible cap 75 closes the archwire slot 74 along the length direction.
In related art, a pair of ends opening in cross section of the archwire slot 74 are provided with stepwise portions 76, 76 for receiving end parts of the convertible cap 75.
The orthodontic appliance 70 is soldered by fusing and filling a silver soldering material between the ends of the convertible cap 75 and the stepwise portions 76, 76, so that the convertible cap 75 is fixed to the main body 72.
The orthodontic appliance 70 furnished with the convertible cap 75 is mainly used to first molars of upper and lower jaws, and is especially called as a convertible buccal tube.
When second molars grow, the convertible cap 75 is peeled off from the archwire slot 74, and the orthodontic appliance 70 is used similarly to an ordinary twin bracket.
In case of being used to other than, for example, the first molars and the second molars of the upper and lower jaws, the orthodontic appliance 70 is called as a convertible bracket.
As the orthodontic appliance furnished with the convertible cap, broadly known are a convertible buccal tube, convertible double tube, convertible twin buccal tube, convertible triple buccal tube, or convertible bracket.
However, the related art orthodontic appliance 70 has been involved with problems as follows.
That is, the related art orthodontic appliance member 70 is not constant in force of peeling the convertible cap 75 from the archwire slot 74. Further, there is a case the soldering is too hard to peel off the convertible cap even with an exclusively used tool (not shown). Moreover, there is a case the convertible cap 75 is carelessly removed from the archwire slot 74 with slight force.
In general, the convertible cap 75 is soldered to the stepwise portions 76, 76 of the main body 72 made of a stainless steel with a dental silver soldering material (BAg-8: Ag 72%, Cu 28%, or BAg-18: Ag 60%, Cu 30%, Sn 10%. However, in a case of fixing it only with the silver soldering material, it is seen that peeling load is largely varied depending on adhering conditions of the silver soldering material filled in a space between the convertible cap 75 and the respective stepwise portions 76, 76 of the main body 72.
The space between the convertible cap 75 and the respective stepwise portions 76, 76 of the main body 72 is mainly created by deformation of the main body 72. Since the deformation is dispersed per each of products or lots, it is extremely difficult to control the peel strength of the convertible cap effecting to the main body 72.
In addition, mainly owing to a galvanic phenomenon by different kinds of metals under conditions in the mouth, a problem has been present in corrosion occurring around soldered parts of the silver soldering material (BAg-8 or BAg-18) of the convertible cap 75.
In other words, two sorts of corrosions have existed from soldered surfaces solidified after fusion and in an interface of the soldered parts.
As to the corrosion from the soldered surface, Cu in the composition of the silver soldering material preferentially elutes, and both of the main body and the convertible cap 75 preferentially elute by influences of the eluted Cu in the interface between the main body 72 and the convertible cap 75 and the silver solder.
Therefore, the soldered strength goes down as time-passing of a teeth curing period, and when a doctor exchanges the archwire, a problem occurs that the convertible cap 75 is carelessly peeled from the archwire slot 74.